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Compatibility of mixed zone constituents (YAG, YAP, YCrO<sub>3</sub>) with a chromia-enriched TGO phase during the late stage of TBC lifetime

Braue, Wolfgang and Mechnich, Peter and Fritscher, Klaus and Niewolak, Leszek (2007) Compatibility of mixed zone constituents (YAG, YAP, YCrO<sub>3</sub>) with a chromia-enriched TGO phase during the late stage of TBC lifetime. Surface and Coatings Technology, 202 (4-7), pp. 670-675. doi: 10.1016/j.surfcoat.2007.07.071.

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The effects of chromia accumulation in the TGO scale of late-stage MCrAlY-based EB-PVD TBC systems are addressed by comparing mixed zone microstructures from isothermal as well as cyclic oxidation tests at 1100 °C with phase relationships derived from the 1100 °C isothermal section of the ternary system Al<sub>2</sub>O<sub>3</sub>-Cr<sub>2</sub>O<sub>3</sub>–Y<sub>2</sub>O<sub>3</sub>. For this approach the c-ZrO<sub>2</sub> phase zirconia coexisting with mixed zone constituents is considered an excess component. Compacted powder pellets were processed via co-decomposition of nitric salt solutions. The reaction products were characterized by X-ray diffraction and Raman spectroscopy. Characteristics of the ternary Al<sub>2</sub>O<sub>3</sub>–Cr<sub>2</sub>O<sub>3</sub>–Y<sub>2</sub>O<sub>3</sub> relevant for the mixed zone include (i) a continuous solid solution series between the orthorhombic phases YAlO<sub>3</sub> (YAP) and YCrO<sub>3</sub>, (ii) a limited Cr vs. Al substitution (16 mol%) in Cr–YAG Y3(Al<sub>1−x</sub>Cr<sub>x</sub>)<sub>5</sub>O<sub>12</sub> and (iii) extended phase fields involving Cr-YAG and sesquioxide phases which represent typical late-stage mixed zones in the excess-zirconia model scenario. The YCrO<sub>3</sub> phase was found to be limited to very chromia-rich environments only. A high chromium enrichment of the mixed zone may be established upon extensive cycling through the miscibility gap in the alumina–chromia system. Later in TBC lifetime the thickness of the mixed zone is increasing due to outward growth of the Al<sub>2−x</sub>Cr<sub>x</sub>O<sub>3</sub> phase into the bottom TBC layer which results in a morphological instability of the TGO/TBC interface.

Item URL in elib:https://elib.dlr.de/52103/
Document Type:Article
Title:Compatibility of mixed zone constituents (YAG, YAP, YCrO<sub>3</sub>) with a chromia-enriched TGO phase during the late stage of TBC lifetime
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Niewolak, LeszekForschungszentrum Jülich, Institut für Werkstoffe und Verfahren der EnergietechnikUNSPECIFIED
Date:November 2007
Journal or Publication Title:Surface and Coatings Technology
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.1016/j.surfcoat.2007.07.071
Page Range:pp. 670-675
Keywords:EB-PVD thermal barrier coatings, TGO, Mixed zone, System Al2O3-Cr2O3-Y2O3, Transmission electron microscopy, Raman spectroscopy
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Aeronautics
HGF - Program Themes:Propulsion Systems (old)
DLR - Research area:Aeronautics
DLR - Program:L ER - Engine Research
DLR - Research theme (Project):L - Combustion Chamber Technologies (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Materials Research > Structural and Functional Ceramics
Deposited By: Mechnich, Dr.rer.nat. Peter
Deposited On:10 Dec 2007
Last Modified:27 Apr 2009 14:31

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